Influence of Environment 



241 



adult, which may be larger or smaller, stronger or weaker, accord- 

 ing as the germ is well or poorly nourished, but it is incredible that 

 the environment which produces rickets, or hypertrophied heart, 

 or loss of sight in one generation should modify the germ cells 

 in such a peculiar and definite way that they should give rise in 

 the next generation to these particular peculiarities, in the absence 

 of the extrinsic cause which 'first produced them. The inheri- 



FIG. 85. GRAFTED FROG EMBRYOS, anterior part, Rana sylvatica, posterior 

 part, R. palustris. In later stages, and even in the adult condition, the two 

 parts preserve their peculiarities. (From Harrison.) 



tance of acquired characters is incredible, because the egg is a 

 cell and not an adult organism ; and in this case there is no suffi- 

 cient evidence that the thing which is incredible really does hap- 

 pen. 



